Method of adjusting radio beacon courses



May 23, 1933. H. DIAMOND METHOD OF ADJUSTING RADIO BEACON COURSES Filed Nov. 24, 1931 4 Sheets-Sheet 1 gwumto p Wm @M.

May 23, 1933. H. DIAMOND 1,910,427

METHOD OF ADJUSTING RADIO BEACON COURSES Filed Nov. 24. 1951 4 Sheets-Sheet 2 FIGURE. 4-

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METHOD OF ADJUSTING RADIO BEACON COURSES Filed Nov. 24. 1931 4 Sheets-Sheet 3 May 23, 1933. H. DIAMOND METHOD OF ADJUSTING RADIO BEACON COURSES Filed Nov. 24; 1931 4 Sheets-Sheet 4 QuAu-ncqvA.

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l atentecl May 23, 1933 i nure s GOVERNMENT OF THE COMMERCE UNITED STATES, REPRESENTED BY THE SECRETARY vrErnon OF ADJUSTING RADIO BEACON COURSES Application filed November'24, 1931. Serial No; 577,026.

(GRANTED UNDER THE ACT OF MARCH 3; 1883, AS AMENDED APRIL so, 1928; 370 0. ($.75?)

The invention described herein may be manufactured and used by or for the Government of the United States forgovernmental purposes only without payment of any I 5 royalty thereon.

This invention relates to improvements in the performance of the double-modulation equisignal type directive radiobeacon whereby it may be successfully employed for proo ducing radio-marked airways coinciding with the fixed airway routes of a given-airways system. More particularly, the inven-' tion relates to methods and apparatus for ad j usting the angles between the courses of the 5 double-modulation beacon so that one, two, three, or even four of these courses may be aligned with the airway routes converging upon the airport at which the beacon is to be located.

0 The double-modulation beacon, when normally adjusted, produces either two or four beacon courses, depending upon whether the carrier frequency currents in the two crossed loop antennas of the beacon station are in 5 time phase or in time quadrature. In the former case the two beacon courses are dis placed in space by 180 degrees, while in the latter case the four courses are displaced in space by 90 degrees. In order to use the 0 beacon practically at any airport, it is necessary to adjust the angles between the courses arbitrarily so as to make them coincide with the airways converging on the airport. These angles are usually different from either 90 or 180 degrees.

1n the early stages of .the double-modulation beacon, before the methods of this invention, and a companion invention by Frank G. Kear, were developed, it was planned to employ the 2-course beacon set-up and to locate the beacon stations at points along the airways half-way between airports, with the beacon courses extending in both directions,

The difficulties of aligning the courses with the airways would thereby be obviated This arrangement, however, had certain im-.

portant disadvantages. The equisignal zones constituting the beacon courses being true angular functions, directly over the beacon tower the courses are of infinitesimal width, while at distances of 100 miles (corresponding to the averagehalf-way distance between two airports) they are of the order of several miles wide. The increasing sharpness of course for decreasing distance from the beacon, coupled with the existence of a zero signal zone directly over the beacon tower,

renders the location of a given point (where the beacon is situated) by an'airplane in flight a relatively easy matter. If this point is,

however, midway between two airports, its location is of little significance. If, however, it is adjacent to one of the airports, the finding of this point permits the pilot to locate the airport under conditions ofpoor visibility. This homing. function is of major importance, being perhaps the most I important and useful feature of the beacon. A second disadvantage of locating the 1 beacons half-way between-airports was that since each beacon served onlytwo courses, the number of stations required for a given airways system were increased.

The methods of aligning the radiobeacon courses with airways converging at arbitrary angles upon a given airport, which are the embodiments of my invention, and the companion invention by Frank G. Kear, permit the location of the beacon station atthe airport.

With the above and other objects in view which will appear as the description proceeds, my invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and,

more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein dis= closed invention may be made as come with in the scope'of the claims. I

The experimental work in connection with this patent having been done on the visual type directive radiobeacon, the methods and apparatus herein described are as used with that type transmitter. It will be understood, however, that these methods also apply to the aural type directive radiobeacon.

For a better understanding of the embodiments of my invention, refer to the accompanying drawings in which like reference characters designate like parts and and like space patterns. Figures 1-6 and 11 relate to introductory material included to facilitate understanding of my invention. Figures 7- 10 describe the embodiments of my invention. Figure 1 shows a schematic diagram of a transmitter and antenna system used for obtaining four beacon courses at 90 with each other. Figures 2 and 3 show the radiated space pattern and the corresponding received polar pattern, respectively, of the double-modulation directive radio range when the antenna currents are 90 out of time phase.

. Figure & shows the received polar diagram when the amplitude of the carrier and side bands of one amplifier branch are reduced Figure 5 shows the received polar diagram when circular radiation of the modulated wave transmitted by one amplifier branch is added to the normal figure-of-eight radiation due to that branch.

Figure 6 shows the received polar diagram when circular radiation in equal amounts of the modulated waves transmitted by both amplifier branches is added to their normal figure-of-eight radiation.

Figures 7 and 8 show the radiated space pattern and received polar pattern, respectively, obtained by reducing the amplitude of carrier and side bands transmitted by one amplifier branch and introducing a circular radiation of the carrier and side bands transmitted by the other amplifier branch in addition to the normal figure-of-eight radiation for that branch.

Figure 9 shows a dia ram illustrating a method for fitting the four beacon courses to four airways.

Figure 10 shows the received polar pattern for serving the four routes simultaneous ly referred to in Figure 9.

Figure 11 is a perspective diagram showing a preferred arrangement of antennas.

For a more complete understanding of my invention, the transmitting circuit arrangement (Figure 1) and the radiated space pattern (Figure 2) and the received polar pat tern (Figure 3) of the t-course double-modulation directive radiobeacon will first be explained.

Referring to Figure 1, a common master oscillator 1 feeds radio frequency power to two intermediate power amplifiers 6 and 7 through the adjustable impedances Z and Z,

respectively. Amplifier 6 is modulated to a low frequency (say, cycles) by means of alternator 8, while amplifier 7 is modulated to a different low frequency (say 86% cycles) by means of alternator 9. The modulated radio-frequency power output of amplifier 6 is fed to power amplifier 10 and then to the primary coil S of a goniometer. Similarly, the modulated radio-frequency power output of amplifier 7 is fed to power amplifier 11 and thence to the primary coil S of the goniometer. The two primary coils together with the two rotor coil systems 14 and 15 serve to transfer the radio-frequency power outputs of amplifiers 10 and 11 to the antennas L and M in such proportion as to orient the beacon space pattern (shown in Fig. 2) in any desired direction.

The function of impedances Z and Z is two-fold; firstly, to control the magnitude of the ff voltages applied to the grids of the intermediate amplifiers 6 and 7 and secondly, to control the phase of these two voltages. By making Z suitably capacitiveoand Z suitably inductive, the desired 90 degree phase displacement between these two voltages may be secured.

Referring to Figure 2, the lines L and M denote the positions of the antennas L and M shown in Figure 1. G denotes the figureof-eight side band characteristic due to w (w =211'f where f is one of the modulation frequencies, say 65 cycles). H denotes a similar characteristic due to (0 (w =..1rf where f is the other modulating frequency, say, 86.7 cycles). K shows the circular carrier space pattern which is called circular because the carrier is a figurc-of-eight revolving at the carrier frequency rate with its successive maxima lying on a circle. The four lines along which-the field intensities of the two modulating frequencies are equal, are indicated by OA, OB, OC, and OD.

The corresponding polar pattern assuming square law detection is shown in Figure 3. G shows the reed amplitude characteristic due to the 65-cycle modulation and H shows a similar characteristic due to the 86.7-cycle modulation. The four courses are indicated by OA, OBQOC, and OD, and are 90 apart.

The trigonometric expression for the beacon space pattern is given in Equation The corresponding expression for the polar pattern as received on the reeds is given in Equation (2).

E [cos wt sin 6+ sin wt cos 6] E1 (1) e =K 2 [cos (ww )tcos (w+w )t] cos 6 [sin (ww )t sin (to w )t] sin 0 where 6 is the field intensity at any point P in space as a polar function of the angle 6, and, as is apparent, consists of a carrier and two sets of sidebands; E /E X100 is the percentage modulation in amplifier branch 1 due to oi E /E X1O0 is the percentage modulation in amplifier branch 2 due to m In this and all the following equations we will assume E =E =E unless otherwise stated. p

GT=KKIEG{E1 Sill. co t Sin? Sill wgt cos 0} .where c is the received signal strength at amplitude of carrier and side bands of one amplifier branch, the polar diagram as received on the reeds is shown in Figure 4, in which G denotes thereed amplitude characteristics due to the 6'5-cycle modulation from the antenna L, and H shows a similar characteristic due to 86.7 -cycle modulation from antenna M. Note that the values of 1x and at; were changed from their 90- value to and 110, respectively.

Another method follows from the companion patent byFrank G. Kear and consists of combining a circular radiation of the carrier and side bands transmitted by one amplifier branch, with the normal figure-ofeight radiation for that branch. A vertical antenna 18, Fig. 1, running the length of the beacon tower and suitably coupled to the output circuit of one of the two amplifying branches of the transmittingsystem, is employed for obtaining this additional radiation. The method of coupling shown in Fig. 1 is inductive, a coil L being connected in series with stator S and placed in inductive relationship with coil L which is connected in series with the vertical antenna 18. It is to be understood that any method of coupling may be employed whereby the current in the vertical antenna is in proper time phase. Assuming a ratio of amplitude of circular radiation to maximum amplitude of figure-of-eight radiation equal to 0.28, the received polar pattern becomes as shown in Figure 5, in which G denotes the resultant reed amplitude characteristic due to the 65- cycle modulation from the antenna L, and the vertical antenna coupled inductively to the amplifying branch having the 65-cycle modulation. H shows the reed'amplitude characteristic due to the 86.7 -cycle modulation from antenna M.

Comparing the received polar diagram of Figure 5 with that of the beacon normally adjusted (see Figure 3), it will be observed that the addition of a circular component to the normal radiation characteristic of the 65-cycle modulated wave results in decreasing the angle B between courses B and C and increasing the angle 13 between the courses, D and A. Note-that the four courses were shifted from their original position.

At certain airports it is desirable to shift two of the four beacon courses from their 180 relationship (viz, B and D) without disturbing the 180 relationship between the other two beacon courses (A and C). This can be accomplished bythe introduction of circular radiation in equal amounts of the carrier and side bands transmitted by both amplifier branches in addition to the'normal fignre-of-eightradiation. One means for accomplishing this is shown in Figure 11.-

The vertical antenna is here placed in inductive relationship with the loop antennas L and M. The degree of coupling to eachof the two-loop antennas determines the amount of 65 and'86 cycle modulation in the. vertical antenna. a The received polar spacepattern for a case of :--this type is shown in Figure 6', in which G denotes the reed amplitude characteristic "due to the 65-cycle modulation, and H denotes a similarbharacteristic due to the 86.7-cycle modulation.

An object of my invention which will now be described is to expand these two methods by combination and otherwise and thereby obtain a more efficient method for aligning the courses of the directive radiob-eacon with airways converging upon a given airport at arbitrary angles. The angles between the airways at a given airport may vary considerably from those at'any other airport. A method more flexible than any of the methods described in the foregoing must therefore be provided, in order to take care of even the more usual cases. My invention provides this method.

' A further object of my invention is the provision of a method for fitting any three of the four radiobeacon courses to airways provided the angles between these airways are within specified limits. I

A still further object of my invention is the provision of a method for aligningthe four beacon courses to four airways provlded the angles between airways are within certain hmits. 1

The theory of operation underlying the portion of my invention which relates to the alignment of three of the four radiobeacon courses with any three airways may be understood from the followinganalysis.

Suppose that the amplitude of carrier and side bands transmitted by one amplifier branch 1s reduced by a reduction factor C and at the same time circular radiation of the carrier and side bands transmitted by the ulated at v(i cycles and Hdenotes, a similar characteristic modulated at 86.7 cycles. K 7

denotes the carrier space pattern.

' The corresponding received polar diagram is: shown in Figure 8, in which G" denotes thereed amplitude characteristic due'tov the (id-cycle modulation and H denotes a simivlar characteristic modulated at 86.7 cycles. -.The trigonometric equation for the radiated space pattern is given by (l3),and for the received pattern by are symmetrical about the O-deg.* 180 deg.

, coursesB and O, and also courses D and A,

axis. This maybe seen byreferenceto Figure 8. The angle between courses B and C is decreased, and the angle between coursesl) I and A increased in hke amount, as the ratioo'lv EH0 cos wtsin 6+ sin wt(K cos 0)] 0 [sin (co w )t sin (02 on) l Sin 6 [cos (w 03 t cos (:0 (.0 t] [K cos 6] Where K Cl rcduction factor for bands due to m I p I I (Ll) e a/(K 1L',, (0 E sin wt sin 0+ I I J 3 E sinwt[1f +cos6]' I In Figures 7 and 8, (1 :0,? and K =.O.22.

Referring to (7) a course will. occur whenever () Ka l-cos 6* U sin 6 Y' I This equation will have four solutions,.one for each quadrant.

In the first quadrant (16) Kg-tcos 6 U sin 6 6 =angle of course A In the second quadrant (17) K cos 0 0 sin 0 6 =angle of course B In the third quadrant (18) li' cos Q U sin 0 course C In the fourth quadrant (19) K +cos 6. sin 6.

course D In (16), (17), (18), and (19) the factors sin 6 cos 6., etc., are constants oi? positive sign.

Subtracting (17) from (16) and solving, We obtain (20) 6 6 =2a where a=tan C carrier and side- 6 angle of 6 angle of "l Similarly, subtracting (19) from (18) and solving, we obtain (21) 6 6 =2a We note, then that the angle between courses A and B, and likewise between courses C and D, are dependent upon C the reduction factor of carrier and sidebands in one amplifier branch. These angles are independent of the amount of circular radiation of carrier and sidebands added to the normal figure-ofeigl1t radiation of the other amplifier branch.

Again, subtracting (18) from (17), and solving, we obtain amplitude of circular radiation due to (0 maximum amplitude of tiguraof-eight radiation due to m:

maximumamplitude of circular to figure-ofbranch is increased. If the phase of the cireight, radiation due to the second amplifier I increase in this ratio will result'in an increase in the angle between courses B and C and a decrease in the angle between D and A. In either case, forav given fixed value of C the angles between the courses A and B and be tween C and 1) remain fixedata value 2 tan" C The procedure of determining the proper values for C and for K in order to serve three courses at given angles with each other is then as follows:

(a) Suppose that courses A and B are deg. apart.

Place 2 tan C =75 deg.

Then C =tan 37.5 deg.=0.767.

(6) Now, suppose that course C is deg. from course B. For convenience in fixing ideas, refer to Figure 8. Under normal adjustments, i. e., with no additional vertical radiation, course 0 would be 105 degrees from course B. To decrease this angle to 90 degrees, circular radiation of proper phase must be introduced. Since B and G are symmetrically disposed about the O-degree180- degree axis, and the angle between courses B and 0 equals 90 degrees, the angle ot'course C must be 295 degrees. Place (c) If course C were to be, say, 120 degrees from course B, the vertical radiation to be introduced must be of the same magnitude as in (b) but of opposite phase. Thus, 0

becomes 240 degrees and K cos 240 deg.= 0.767 sin 240 deg.

(d) Suppose that an angle of'165 degrees between courses B and C were desired. Course D is normally 180 degrees from B and is therefore the course to be used, with the proper amount of circular radiation introduced to obtain the desired angular shift. Courses D and A are symmetrically displaced about the 0-degree180-degree axis and course A is 7 5 degrees from B. The angle of course D is therefore 6 300 deg. and

K cos 300 deg.= 0.767 sin 300 deg.

' IQ-l- 0.50 -().665

Note that for this value of K course C is 120 degrees from B.

The limits for the method of aligning three of the four beacon courses with the airways arbitrary angles are tabulated below. These limits are based on two criterions: (1) the signal strength received when on any given course should not be reduced below per cent of that received when the four courses are displaced by 90; (2) a deviation of at least 20 on either side of the beacon course should be possible without losing indications as to the direction back to the course. three airways are called A, B, and C, respectively.)

With these two criterions in mind any two of the three airways (say A and B) may be from degrees to 90 degrees apart. The third airway (C') may then be disposed from either A or B by any angle within the ran e given in the table. As shown, the practicable range of angles between C and either A or B depends upon the anglevbetween A and B. A greater variation can of course be obtained if it is permissible to reduce the signal strength received when on course. The third column of Table I shows the possible range if the minimum permissible signal strength when on any given course 1 1s taken as 33 per cent of normal.

(F or convenience in tabulation the Table 1 Range of permissible angles Range of permissible angles The method for aligning the four beacon courses to four airways converging at an airport at arbitrary angles is accomplished by reducing the amplitude of the carrier and side bands of one amplifier branch and also introducing circularradiation of the carrier and side bands transmitted by one or both amplifier branches in addition to their nor- 7 mal figure-of-eight radiation.

A typical example will best explain this method for shifting the beacon courses so,

that they may coincide with the four airways radiating from a given airport. Considering a station set up at College Park, Md,

suppose that it is desired to direct courses on V Hatboro, Pa, Norfolk, Va, Quantico, Va.,. and Bellefonte, Pa. The bearings of these cities from College Park are, respectively,

'Degrees Hatboro, Pa 48.5 Norfolk, Va i 160.5 'Quantico, Va. 219.5 Bellefonte, Pa. 343.

These courses are plotted in Figure 9,-the angles between these courses'being as indicated. The four courses can obviously be approximated by'the method of amplitude reduction (method A) for shifting courses. Thus, draw line AC through the origin, equally'displaced from the courses to Hat-- boro, Pa.,and Quantico, Va. Also-draw line BD through the origin, equally displaced from the courses to Norfolk, Va., and Bellefonte, Pa. The angle between these two lines is 62.2 deg. Placing tan C =62.2 deg. where C is the reduction factor for the car rier and sideband in'amplifier branch 2,"we obtain" '7 I It is now necessary to introduce sufiicient circular radiation of both modulated wavesto make courses A, B, C, and D coincide with to make courses A and D symmetrical about the 0 deg.-180 deg. axis (see Figure 4). Subdesired courses stituting the bearings for the courses to Hatboro, Pa., and Norfolk; Va, in (27) we have K -l-sin (48.5 cleg.l2.9 deg.)

K 0.603 cos (e85 deg. 12.9 deg.)

K +sin (160.5 deg.12.9 deg.)

K +0.6O3 cos (160.5 deg.12.9 deg.) Solving K 0.060 K =O.038.

The corresponding angular setting of the vertical antenna coupling coil (Figure 19) is easily computed. The resultant space pattern is given in Figure 10.

While I have described my invention in certain of its preferred embodiments I desire that it be understood that modifications may be made and that nolimitations upon my in- 20 ventions are intended other than are imposed by the scope of the appended claims.

What I claim is:

1. A method of aligning a plurality of beacon courses With a plurality of airways converging at an airport which consists in reducing the amplitude of the carrier and side bands of one amplifier branch and also introducing circular radiation of the carrier and side bands transmitted by one or both amplifier branches in addition to their normal figure-ot-eight radiation.

2. A method of changing the angular di rections of three equisignal lines of a double modulation equisignal type of directive radio beacon which consists in first placing two of the three courses at the proper angle by properly reducing the carrier and side band of one amplifier branch and then through the addition of circular radiation of the carrier and side band in the vsecond amplifier branch placing the third course at the desired angle with respect to one of the first two courses. 7

3. A method of changing the angular directions of four equisignal lines of a doublemodulation equisignal type of directive radio beacon which consists in first changing the orientation of the beacon space pattern so that two one hundred eighty degree equisignal lines are displaced by equal angles from two of the airways; second, reducing the amplitude of the carrier and side bands transmitted by one amplifier branch of the beacon so that a second set of one hundred eighty degree equisignal lines is displaced by equal angles from the second set of airways to be served; and third,by introducing the proper amounts of circular radiation of the carriers and side bands of both amplifier branches so that each one of the equisignal lines is made to coincide with a corresponding one of the four airways to be served;

I11 testimony whereof I afiiX my signature.

HARRY DIAMOND. 

